Elements 113 And 115 Discovered

From: William Wise <w.wise.nul>
Date: Sun, 1 Feb 2004 14:07:25 -0500
Fwd Date: Sun, 01 Feb 2004 16:05:19 -0500
Subject: Elements 113 And 115 Discovered
Source: The New York Times
http://www.nytimes.com/2004/02/01/science/01ELEM.html
February 1, 2004
Uut and Uup Add Their Atomic Mass to Periodic Table
By James Glanz
A team of Russian and American scientists are reporting today
that they have created two new chemical elements, called
superheavies because of their enormous atomic mass. The
discoveries fill a gap at the furthest edge of the periodic
table and hint strongly at a weird landscape of undiscovered
elements beyond.
The team, made up of scientists from Lawrence Livermore National
Laboratory in California and the Joint Institute for Nuclear
Research in Dubna, Russia, is disclosing its findings in a paper
being published today in Physical Review C, a leading chemistry
journal. The paper was reviewed by scientific peers outside the
research group before publication.
"Two new elements have been produced," said Dr. Walt Loveland, a
nuclear chemist at Oregon State University who is familiar with
the research. "It's just incredibly exciting. It seems to open
up the possibility of synthesizing more elements beyond this."
The periodic table is the oddly shaped checkerboard =97 with an H
for hydrogen, the lightest element, in the upper-left-hand
corner =97 that hangs in chemistry classrooms the world over. Each
element has a different number of protons, particles with a
positive electrical charge, in the dense central kernel called
the nucleus.
The number of protons, beginning with one for hydrogen, fixes an
element's place in the periodic table and does much to determine
an element's chemical properties: ductile and metallic at room
temperature for gold (No. 79), gaseous and largely inert for
neon (10), liquid and toxic for mercury (80).
Elements as heavy as uranium, No. 92 on the list, are found in
nature, and others have been created artificially. But much
heavier elements have been difficult to make, partly because
they became increasingly unstable and short-lived.
Still, for roughly half a century, nuclear scientists have been
searching for an elusive "island of stability," somewhere among
the superheavies, in which long-lived elements with new chemical
properties might exist. Dr. Loveland said that the new results
indicated that scientists might be closing in on that island.
"We're sort of in the shoals of the island of stability," said
Dr. Kenton J. Moody, a Livermore nuclear physicist who was one
of the experimenters in the work.
"It's an amazing effect," he added. "We're really just chipping
away at the edges of it."
The experiments took place at a cyclotron, a circular particle
accelerator, in Dubna, where the scientists fired a rare isotope
of calcium at americium, an element used in applications as
varied as nuclear weapons research and household smoke
detectors. Four times during a month of 24-hour-a-day
bombardment in July and August, scientists on the experiment
said, a calcium nucleus fused with an americium nucleus and
created a new element.
Each calcium nucleus contains 20 protons and americium 95. Since
the number of protons determines where an element goes in the
periodic table, simple addition shows the new element to bear
the atomic number 115, which had never been seen before. Within
a fraction of a second, the four atoms of Element 115 decayed
radioactively to an element with 113 protons. That element had
never been seen, either. The atoms of 113 lasted for as long as
1.2 seconds before decaying radioactively to known elements.
Scientists generally do not give permanent names to elements and
write them into textbooks until the discoveries have been
confirmed by another laboratory. By an international convention
based on the numbers, element 113 will be given the temporary
name Ununtrium (abbreviated Uut for the periodic table) and
element 115 will be designated Ununpentium (Uup).
Dr. Loveland said he agreed that the new elements would require
independent confirmation before they could receive final
acceptance. And he conceded that the Dubna find was likely to
receive more than the usual amount of scrutiny: two years ago,
the reported discovery of Element 118 was retracted after a
scientist at Lawrence Berkeley National Laboratory was found to
have fabricated evidence.
The only other truly simultaneous discovery of two elements in
recent times came in 1952, when einsteinium (99) and fermium
(100) were discovered in the fallout from the hydrogen bomb
explosion at Eniwetok Atoll in the Pacific Ocean. The most
recent successful discovery of an element =97 one that has
received a name =97 came in 1994. That element, No. 110, is called
Darmstadtium for the city in Germany where it was discovered.
But as scientists wait for confirmation on elements 115 and 113,
the data presented by the Dubna and Livermore groups appear
solid, said Dr. Sigurd Hofmann, a nuclear physicist at the
Institute for Heavy Ion Research in Darmstadt, the laboratory
where Darmstadtium was found.
"These Dubna data look quite convincing," Dr. Hofmann said. "And
I'm sure with some more experiments, it will finally be
accepted."
Dr. Joshua B. Patin, a 28-year-old nuclear chemist who is the
lead American author on the paper, said he had found it deeply
moving to add two more entries to a scientific icon that dates
to the 1860's. That was when the Russian chemist Dmitri
Ivanovich Mendeleyev noted clear patterns in the chemical
properties of the known elements and arranged them into the
periodic table, leaving gaps for other elements that he
correctly predicted would someday turn up.
"This is a working piece of art," Dr. Patin said. "We're not
done yet. Nothing's been finished. What it could really mean
down the road, nobody can tell. And that's the part that's
exciting to me."
The lead authorship on the work went to Dr. Yuri Oganessian,
scientific director of the Flerov Laboratory of Nuclear
Reactions at the Joint Institute for Nuclear Research in Dubna,
whose theoretical research in the 1970's revealed the path that
eventually led to the most recent discoveries.
The experimental group that Dr. Oganessian leads is especially
skilled at using extremely small amounts of the rare calcium
isotope in the bombardment and at filtering out signals from
just a handful of new atoms among the debris spewing from the
collisions.
"These elemental discoveries underscore both the value of
federally supported basic research and the benefit of unfettered
international scientific collaboration," said Energy Secretary
Spencer Abraham, whose agency helped finance the work.
In a written response to questions, Dr. Oganessian said the
results "favor the conclusion about the formation of a new
element and refute any other interpretation." He added that
confirmation of the work was necessary, but that everything had
been done to ensure that the analysis was correct.
"In order to exclude the human factor," Dr. Oganessian said,
"the analysis of the data is carried out in parallel and
independently by the two groups in Dubna and in Livermore."
Physicists long ago discovered that atomic nuclei have what came
to be known as "magic numbers." Nuclei that contain just those
numbers of protons and their electrically neutral cousins,
neutrons, are especially stable. The numbers 2, 8, 20, 28, 50,
82 are magic for both protons and neutrons.
Theoretically, those numbers come about because nuclei have a
shell-like structure, said Dr. Witold Nazarewicz, a nuclear
theorist at the University of Tennessee and Oak Ridge National
Laboratory. Each shell can hold particular numbers of protons
and neutrons, and a nucleus is most stable when its shells are
precisely filled up, leading to the magic numbers.
The highest known magic number for neutrons is 126, meaning that
common lead, with 82 protons and 126 neutrons in its nucleus is
the heaviest known "doubly magic," or extremely stable, isotope
in the periodic table.
"The question is, what is the next doubly magic nucleus beyond
lead?" Dr. Nazarewicz said.
Those numbers should help map out what Dr. Nazarewicz prefers to
call generically a "region of stability" among the superheavies.
(Because, he says, it could resemble a peninsula more than an
island.) Various theories have suggested that the next magic
proton number is 114, 120 or 126, he said. There is general
agreement that the next magic neutron number is 184, he said.
The new experiments by the Livermore and Dubna scientists
created forms of element 115, for example, with at most 173
neutrons, suggesting that they are still short of what could be
a land of strange new forms of matter.
Rather than being round, nuclei in that region and beyond could
contain bubbles and have strange doughnut-like shapes, Dr.
Nazarewicz said.
They could also have unpredictable chemical properties.
The new work should shed light on whether theories of those
undiscovered bits of matter are correct or not, he said.
"Those discoveries tell us a great deal about the underlying
nuclear structure," Dr. Nazarewicz said. "About how the very
heaviest systems are built =97 how they tick."
Dr. Darleane C. Hoffman, a nuclear chemist at the University of
California, Berkeley, also cautioned that the new findings would
have to be checked out by other laboratories. But she said the
value of the work was unquestioned.
"Scientifically, just for the pure science of it, wouldn't you
like to know just how many chemical elements there are?" Dr.
Hoffman said. "And until you actually have a measurement that
you believe and you can confirm, you don't have any idea whether
the various models the theorists propose have any meaning at
all."